Environmental and Alloying Effects on Corrosion of Metals and Alloys

by Dong Liang

Institution: The Ohio State University
Department: Materials Science and Engineering
Degree: PhD
Year: 2009
Keywords: Materials Science; Chromium free welding consumable; Ni-Cu-Pd; Ni-Cu-Ru; Gas Tungsten Arc Welding (GTAW); Shielded Metal Arc Welding (SMAW); Atmospheric corrosion; Ag; Galvanostatic reduction method; NaCl particles; Thermophoretic deposition method; UV; Relative Humidity
Record ID: 1863833
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=osu1243995273


Occupational Safety & Health Administration (OSHA) under U.S. Department of Labor released a new regulation which required a substantial reduction of the permissible exposure limit (PEL) of Cr6+ from 52 µg/m3 to 5 µg/m3 to protect the workers’ health. Ventilation of the hazardous welding fumes is difficult because manual SMAW is often used in confined spaces during ship-building process. Since the main source of fumes is the melting filler metal, therefore the aim is to develop a chromium-free filler metal for welding of SS304 as a replacement for conventional SS308 while retaining the corrosion properties. In the first part of this project, corrosion studies were carried out on 304L stainless steel samples welded with Cr-free consumables, which were developed to minimize the concentration of chromate species in the weld fume. The corrosion properties of Ni-Cu and Ni-Cu-Pd Gas Tungsten Arc (GTA) welds and Shielded Metal Arc (SMA) welds are found to be comparable to those of welds fabricated with SS308L consumable. Due to the cost of recently-developed Ni-Cu-Pd weld consumables, efforts have been made to find a substitute for Pd using other relatively cheaper elements while retaining satisfactory corrosion and welding performance. Ru is chosen because it is the cheapest in the Platinum Group Metal. The results suggest that Ni-Cu-Ru welds exhibited comparable or even better corrosion properties than SS308L and Ni-Cu-Pd welds. In the second part of this project, efforts are put on the connection between lab and field exposure tests because sometimes the correspondence between lab atmospheric corrosion tests (ASTM B117) and field exposures is poor as a result of differences in the critical conditions controlling chemical and electrochemical reactions on surfaces. Recent studies in atmospheric chemistry revealed the formation of reactive species from interactions between UV light, chloride aerosols and oxidizing agents such as ozone. Atmospheric corrosion can be affected by these species which might be transported long distances in the atmosphere. However, these species could be missed in ASTM B117 test. Initial efforts focused on the effects UV radiation, O3, relative humidity (RH) on the atmospheric corrosion of bare silver. It was found that both UV and O3 are necessary for fast corrosion on bare silver and this fast corrosion reaction results from atomic oxygen generated photodegradation of O3. In the presence of UV and O3, RH has little effect on the atmospheric corrosion of bare silver. Later, focus was put on the atmospheric corrosion of silver with nanometer-sized NaCl particles deposited on the surface. O3 was found to cause corrosion of silver with NaCl particles even in the absence of UV. The enhancement of corrosion by UV is limited for Ag with NaCl particles at low ozone concentration and high RH. The corrosion rate of silver with NaCl particles is found to increase with RH. Finally, bare silver samples were exposed in salt spray chamber according to ASTM B117 up to 4 months. Very…